Generalized recombination is a fundeamental mechanism for generating genetic diversity and for the responses to blockage of DNA replication. Three pathways for generalized recombination are known in E. coli. We will investigate the substrate requirements and the structure of the recombination intermediates and products of each pathway. The model system used is the recombination between plasmids and phage in vivo. The recombination process will be studied primarily through a biochemical, structural approach, with genetic and enzymological approaches to complement it. The long-term goal is to achieve a detailed understanding of the mechanisms for generalized recombination in E. coli, via in vitro recombination that is faithful to the in vivo process. We will also apply generalized recombination to powerful new methods for the screening of phage and plasmid libraries. These methods promise to make library screening faster, easier, and cheaper.